Modern vehicle bodies are provided with a very rigid chassis-subframe in the region of the front wheel suspension, whereby the absorption of transverse forces and thus the directional stability of the vehicle is improved. Moreover, in this design the entire drive train, including the front wheel suspension, is able to be fitted in a manner that is advantageous in terms of production technology as a complete assembly module into the vehicle body during the vehicle assembly.
However, this design results in problems relative to the crash protection of the vehicle occupants. Thus, for the protection of the vehicle occupants, in particular in the case of a front impact of the vehicle, a number of measures are known from the prior art in which the kinetic energy of the vehicle is converted into deformation energy by the plastic deformation of body parts, and too great an acceleration of the occupants is intended to be prevented thereby. When fitting a chassis-subframe, however, the rigidity thereof, which is actually desired to improve the directional stability, prevents the deformation zones of the body in the region of the subframe from being able to deform sufficiently.
EP 1 510 444 B1 discloses, for example, a chassis-subframe arrangement for improving the crash protection for vehicles, in which a chassis-subframe that is fastened directly to load-bearing body parts is detached from the body parts and displaced to the rear in the event of a front impact of the vehicle. In this case, at its rear suspension points viewed in the vehicle longitudinal direction, the subframe is pushed below the passenger compartment by a ramp formed by the load-bearing body parts. At its rear suspension points the subframe is indirectly connected to the load-bearing body parts via a fastening plate weakened by longitudinal forces, said fastening plate being correspondingly deformed in the case of a displacement movement of the subframe directed to the rear.
Moreover, a front part structure of a vehicle body with a chassis-subframe is disclosed in EP 2 017 163 B1, said front part structure being connected at rear suspension points via fastening means directly to the vehicle body. In the event of a front impact of the vehicle, the subframe is detached from the vehicle body at its rear suspension points.
U.S. Pat. No. 5,884,963 discloses a body structure element which, in the event of a front impact of the vehicle, converts kinetic energy by the deformation thereof and by further deformation conducts a chassis-subframe below the passenger compartment.
U.S. Pat. No. 8,646,792 B2 discloses a vehicle frame structure with a chassis-subframe, an absorption surface interacting therewith in the case of a displacement movement of the subframe as a result of a front impact of the vehicle, in order to convert kinetic impact energy by additional deformation work.
For improving the crash protection, accordingly it is generally provided that in the event of a front impact of the vehicle, from a specific degree of deformation of the body parts, the chassis-subframe is detached from the vehicle structure and is pushed to the rear below the vehicle structure relative to the vehicle longitudinal direction. In this case, the fastening means, for example mounting bolts, with which the chassis-subframe is usually fastened to high load-bearing parts of the vehicle body, either pull out of or shear off the load-bearing body parts. By the current intensive use of, for example, boron steels, which have the characteristic of being brittle, for producing the high load-bearing body parts, there is the risk of the load-bearing body parts being cracked or even ruptured, however, when in the event of a front impact of the vehicle, the fastening means of the chassis-subframe is pulled out of the body part. This, however, results in significant weakening of the load-bearing body parts and thus of the deformation zones of the vehicle. Moreover, after the detachment of the subframe and its displacement below the vehicle body, there is also the risk that the pulled-out fastening means, for example the screw bolts, in the course of their displacement interact with other load-bearing body parts, for example by becoming caught thereon, whereby the load-bearing body parts are also able to be damaged by the aforementioned effect and thus weakened.